12 13题求解答.必最佳.
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12 13题求解答.必最佳.
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再答: F(X)=1/3 aX3 1/2aX2-2aX 2a 1 F’(X)=aX^2 aX-2a=a(x 2)(x-1) 在x=-2,x=1处有极点, 且f(-2)=16a/3 1,f(1)=5a/6 1, f(0)=2a 1 1.a>0时, x<-2时,f(x)不过第四象限; -2<x<0时,f(x)不过第四象限; 0<x<1时,f'(x)<0,f(x)递减,5a/6 1<f(x)<2a 1,因a>0,f(x)不过第四象限; x>1时,f'(x)>0,f(x)递增,f(x)>5a/6 1,因a>0,f(x)不过第四象限. 2.a<0时, x<-2时,x在二三象限,f'(x)<0,,f(x)递减,f(x)>16a/3 1; -2<x<0时,x在二三象限,f'(x)>0,,f(x)递增,16a/3 1<f(x)<2a 1; 0<x<1时,x在一四象限,f'(x)>0,f(x)递增,2a 1<f(x)<5a/6 1,f(x); x>1时,x在一四象限,f'(x)<0,f(x)递减,f(x)<5a/6 1, 所以a<0, x<0,x在二三象限,16a/3 1<f(x)<2a 1,f(x)过二三象限的充要条件是16a/3 1<0,2a 1>0,-1/2<a<-13/16 x>0,x在一四象限,2a 1<f(x)<5a/6 1,f(x)过一四象限的充要条件是5a/6 1>0,2a 1<0 ,-6/5<a<-1/2 snyhs | 2009-06-04 29 0